1. Field of the Invention
The present invention relates to toolholders and toolholder support members used in the metalworking industry. In particular, the subject invention is directed to a secondary retention system that restrains a toolholder within a toolholder support member once the primary retention system has released the toolholder. The secondary retention system provides a machine tool operator with the opportunity to remove the toolholder from the toolholder support member in a controlled fashion.
2. Description of Related Art
U.S. Pat. No. 4,747,735 entitled “Toolholder and Method of Releasably Mounting” by Erickson, et al., which patent is assigned to the Assignee of the present application and the contents of which are hereby incorporated by reference, discloses a toolholder secured within a toolholder support member through radially displaceable locking balls which engage perforation surfaces within the shank of the toolholder to provide a primary retention system. A simplified version of the toolholder illustrated in the '735 patent is shown in FIGS. 1 and 2. In particular, the toolholder support member 210 receives the shank 215 of a toolholder 225 through face 211, 231 contacts between the toolholder 225 and toolholder support member 210 in the region 235. Additionally, there is a resilient interference fit between the shank 215 of the toolholder 225 and the wall 232 of the bore 233 of the toolholder support member 210. This mechanism for securing the toolholder 225 to the toolholder support member 210 is the primary retention system. When the toolholder 225 is removed from the toolholder support member 210 (FIG. 2), in order to overcome the resilient interference fit, the toolholder 225 is positively displaced using a bump-off mechanism 240 within the toolholder support member 210. Once the toolholder 225 is bumped-off from the toolholder support member 210, as illustrated in FIG. 2, the toolholder 225 is unrestrained within the bore 233 of the toolholder support member 210. In a most revealing example, if the toolholder 225 is vertically beneath the toolholder support member 210, then upon release, the toolholder 225 may freely fall from the support member 210. In some circumstances, the toolholder 225 may be fairly heavy and the machine tool operator may be required to use one hand to deactivate the primary retention system and the other hand to support the toolholder 225. The primary retention system is comprised of locking balls 245 that are radially activated by the lock rod 250 to engage forwardly facing surfaces 255 within the perforations 257 of the shank 215 of the toolholder 225. These locking balls 245, in conjunction with the face 211, 231 contacts and resilient interference fit, securely hold the toolholder 225 within the toolholder support member 210. However, once again, once the toolholder 225 is displaced from the toolholder support member 210, it is unrestrained and it is important for the operator to have full control over the toolholder 225 once it is released from the toolholder support member 210.
Under certain circumstances, a system is needed to provide a secondary retention to the toolholder once it is released from the primary retention of the toolholder support member.